Better gang allies handling

So I can damage and be damaged by members of an allied gang of an allied gang of my gang, etc. It would be better I couldn't damage and be damaged by members of an allied gang of an allied gang of my gang, etc..

Spoiler: You don't really need it, but I wrote this

Something like that in your gang class:

Code:

public List<UUID> getAllies() {
    List<UUID> allies = new ArrayList<>();
    allies.addAll(getMembers());
    getAlliedGangs().forEach(g -> {
        g.getAllies().forEach(ap -> {
            if(!allies.contains(ap)) {
                allies.add(ap);
            }
        });
    });
    return allies;
}
public boolean isAlly(UUID player) {
    return getAllies().contains(player);
}

And then in your EntityDamageByEntityEvent listener get damager's gang and do if(<gang>.isAlly(<damaged entity>.getUniqueId())) cancel the event and do your things like sending messages, etc.
NOTE: I didn't see your gang class, so this code may be wrong.
NOTE: You need to prevent cycling allied gangs.